Adapted Full-Season Cultivars Maximize Soybean Yield Potential At Optimum Planting Dates.

Over the last decade, researchers in the U.S. Corn Belt states have updated soybean [Glycine max (L) Merr.] planting date guidelines based on research showing maximum yields with late April to early May plantings, with yield losses accelerating as planting is delayed through May and into June. This has encouraged earlier planting, which in turn raises questions about the interaction between planting date and other management factors. Our objectives were to determine the effect of cultivar maturity selection and fungicide + insecticide seed treatments on yield of soybean planted early and at more typical planting times. The experiments were conducted at a total of 57 sites in 2011 and 2012, in cooperation with volunteer grower cooperators in Illinois and Indiana. At each site, a short-season cultivar and an adapted, full-season cultivar were planted with and without fungicide + insecticide seed treatments, at an early and normal time. Planting dates were 23 April and 17 May for the early and normal planting time, respectively, across sites. The 2011 growing season was characterized by very high spring precipitation, but good conditions during most of the growing season, while 2012 was one of the warmest and driest seasons on record. When planted at the early date, full-season cultivars produced 236 and 424 kg ha^-1 more grain than short-season cultivars in 2011 and 2012, respectively. In 2011, early planting increased the yield of full-season cultivars by 343 kg ha^-1 over the normal planting time, but planting time did not affect yield of short-season cultivars. In 2012, planting time had no effect on yield of full-season cultivars, but early planting reduced the yields of the short-season cultivars by 182 kg ha^-1. Seed treatment did not interact with planting time, but increased yields in 2012 by 74 kg ha^-1. These results indicate that planting full-season, adapted cultivars early maximizes the chance of highest yields, and minimizes the chance for yield losses under certain unfavorable conditions.